1. Field of the Invention
The present invention relates to a computer system having a memory card or a small-sized hard-disk drive as an external storage device.
2. Description of the Related Art
A conventional computer system, e.g. a portable computer, employs, as an external storage device, a small-sized hard-disk drive (HDD) including, e.g. a 2.5-inch disk. Compared to a floppy-disk drive (FDD), HDD has advantages, i.e. a larger capacity and a higher access speed.
However, the disk used in HDD cannot be replaced, whereas a floppy disk used in FDD as memory medium can easily be replaced. Although HDD can be replaced as a whole unit, users cannot easily replace it.
On the other hand, systems using a memory card as external storage device, other than HDD and FDD, have been developed. The memory card is a memory device wherein a thin card-like casing contains a circuit board on which memory ICs are mounted.
Like the disk in FDD, the memory card is easily replaceable. In addition, the memory card has a higher access speed than HDD. At present, however, the memory capacity of the memory card is smaller than that of HDD or FDD.
There have already been specification standards for memory cards, based on JEIDA (Japan Electronic Industry Development Association) and PCMCIA (U.S.A.) (Personal Computer Memory Card International Association). The specification standards based on JEIDA and PCMCIA are partially common.
There is an idea that both a replaceable memory card with high access speed and HDD with large memory capacity are commonly used in a system. In such a case, however, the size of the system increases and the manufacturing cost of the system also increases.
It is ideal, therefore, to use the memory card or HDD selectively as external storage device, depending on the need. In order to achieve this, it is necessary to solve technical problems, thereby realizing easy replacement of HDD and easy mutual exchange of the memory card and HDD.